Impedance matching device



Dec. 21, 1948. J. B. DEARING I -2,456,770

IMPEDANCE MATCHING DEVICE Filed Feb. 14, 1944 Y. Livy/v5. EMF/N5'(Ittomeg Patented Dec. 21, 1 948 John B. Dearing,

Haddonfield, N. 1.,yassignor to Radio Corporation of America, acorporation of Delaware Application February 14, 1944, Serial No.522,224

1 Claim. 1

This invention relates to artificial load devices.

Artificial loads for sources of high frequency electrical energy,constructed according to the prior art, consist generally of resistorswhich at high frequencies exhibit substantial reactive characteristics.Such resistors are not only highly cumbersome, but it is also difilcultto tune them to a point of minimum reactance. The device of the presentinvention may be used as an artificial load.

An object of this invention is to provide an improved high frequencydevice which is more accurate, compact, and adjustable over a verysubstantially greater range of frequencies than devices of the priorart.

A further object of the invention is to provide an improved and compactartificial load for a source of high frequency electrical energy.

The invention may be better understood fromv a reading of the followingdescription of an embodiment thereof, and from a consideration of theaccompanying drawing, in which the figure is a sectional view inelevation of an artificial load constructed according to the invention.

A device constructed in accordance with the invention Will operatesatisfactorily as an artificial load for a source of highfrequencyenergy. It is desirable to use for artificial loads materialswhich have a high resistance to such currents. Magnetic materialsgenerally exhibit this property of high resistance and, in particular,iron and cold-rolled steel, which are cheap and readily available. Thefigure is a sectional view in elevation of an artificial loadconstructed in accordance with the invention. The inner conductor I andintermediate conductor 3 are contained within the outer conductor 5, andthe length of the inner conductor I within the other conductors is madevariable. A conductive end piece 1 is secured at one end of the outerconductor, as by the screws 9a, 9b. The end piece has an aperture I I ofthe same diameter as the inner conductor I, so that the inner conductormay slide in the aperture and at the same time make good contact withthe end piece, and so that the length of the inner conductor within theouter and intermediate conductors may be varied. A locking screw Isecures the inner conductor in any desired position. Insulating spacers51 separate the intermediate and outer conductors. A transmission line59. having an outer member GI and an inner member 63, connects thesource of high frequency energy to the load; it is desirable to coupleinto or tap the concentric line at a point whose impedance matches thatof the transmember 6| to the outer conductor 5, connection being made byany standard transmission line coupling 65. A short-circuiting cylinder61, having an insulated handle 69, is inserted at the open end of theconcentric line and serves to connect the outer and intermediateconductors at that end at points which may be varied by moving thecylinder. Such movement varies the impedance which the load presents tothe transmission line, and provides a means for matching the impedanceof the load to that of the line. Hence, both the cylinder 61 and innerconductor I are calibrated in terms of the frequency at which the loadpresents the desired impedance to the transmission line.

The cylinder may be maintained in any desired position, as by set screws11. A lamp I! may be connected across the circuit.

In operation, inner conductor I and cylinder 61 are each set at theknown frequency of the source of high frequency energy, and the load isthen coupled to the source. While the lamp lI may be used to indicateresonance, this is not strictly necessary, because if inner conductor Iand cylinder 67 are properl calibrated, the load will be matched to theline at the frequency of the source. The light intensity of lamp II isproportional to the power dissipated in the load, and the light maytherefore, if desired, be transmitted to a photometer, and used as ameasure of such power. If power in excess of 50 watts is dissipated inthe load, it will be desirable to cool the latter, as by means ofair-cooling fins, a water jacket or the like.

Thus a high frequency device has been described in which a foldedconcentric line has been employed as the resonant circuit. The deviceis, by means of the folding, substantially more compact than prior artdevices which include concentric lines. A device constructed inaccordance with the invention may be used as an artificial load for asource of high frequency energy.

I claim as my invention:

Apparatus of the character described, comprising in combination a sourceof high frequency electrical energy, a concentric resonant lineconstituted by an outer hollow cylindrical conductor, a calibrated innerconductor contained within and concentric with said outer conductor andan intermediate hollow cylindrical conductor nested between andconcentric with and radiall spaced from said inner and outer conductors,said conductors being composed of material having a high resistance tohigh frequency currents, said line having an open end and a closed end,a conductive end member at said closed end having an aperture therein,said inner conductor being of equal diameter with an slidable withinsaid aperture whereby to form an adjustable connection at said closedend between said inner and outer conductors, said intermediate conductorextending from said open end towards, but spaced from, said end member,a connection from said source to said line, and a slidable calibratedshort-circuiting cylinder adapted to be inserted between said outer andintermediate conductors at said open end to form an adjustableconnection between said outer and intermediate conductors.

JOHN B. DEARING.

REFERENCES CITED The following references are of record in the fileof'this patent:

UNITED STATES PATENTS Number Name Date 2,171,219 Malter Aug. 29, 19392,236,004 MacLean Mar. 25, 1941 2,276,743 Shimizu Mar. 1'7, 19422,294,881 Alford Sept. 8, 1942 2,306,282 Samuel Dec. 22, 1942 2,349,440Lavoie May 23, 1944

